The present invention relates to sensor components and especially to sensor components with an improved and more reliable contact arrangement between the sensor and connecting wires attached thereto.
Sensor components are nowadays used e.g. as temperature sensors or also as air- or gas-flow sensors. For detecting a temperature, temperature sensor components made of platinum are, for example, used for determining the ambient temperature. A platinum temperature sensor component functions such that a temperature variation in the surroundings of the platinum temperature sensor component causes a resistance change in a platinum film arranged in the component. This resistance change can be detected by a measuring circuit and evaluated with respect to the ambient temperature so that the temperature of the surroundings in which the platinum temperature sensor component is arranged can be determined.
A conventional platinum temperature sensor component is shown in FIG. 5. A support material 2 consisting of a ceramic material, e.g. Al2O3 ceramic, has applied thereto a structured platinum film 4. In a connection and contact area two connecting wires 6 are electrically connected to the platinum film 4. A fixing glaze 8 is applied to the connecting wires 6 and the platinum film 4 in the contact area. Outside of the contact area, the platinum film 4 is coated with a glass passivation layer 10 so as to protect the plastic film 4 against environmental influences. The fixing glaze 8 is provided for mechanically fixing the connecting wires 6 to the sensor component via this glaze composition applied to the contact area.
This configuration provides a sufficient and reliable contact quality for many cases of use. For very difficult cases of use with high mechanical, thermal and chemical loads on the sensor component, this configuration will, however, entail substantial limitations.
The contact quality between the connecting wires 6 and the sensor component is essentially determined by the adherence of the platinum film 4 to the ceramic support 2. The originally sufficient adherence of the platinum film 4 can, however, be markedly reduced or even disappear e.g. due to slightly different coefficients of thermal expansion of the ceramic material (e.g. Al2O3 ceramic) and of platinum, due to frequently occurring and extreme temperature variations (20xc2x0 C. to 800xc2x0 C.) and due to simultaneously occurring outer mechanical strains or loads or due to an aggressive ambient chemical atmosphere. When the sensor components are exposed to adverse conditions for a very long period of time (e.g. months, years), this may lead to electrical as well as mechanical contact problems in the contact area between the connecting wires 6 and the platinum film 4.
Since the sensor components are frequently exposed to very hard mechanical, thermal and chemical loads in practical use, these high loads will normally affect both the actual sensitive area and especially also the contact zone of the outwardly extending electrical connections.
Since the individual layers of a conventional platinum temperature sensor component are arranged one on top of the other with open lateral parting layers, disturbing environmental influences may additionally act on the sides of the exposed individual edges of the superimposed layers. Over a prolonged period of time, this may cause damage to the platinum layer and it may also cause the platinum layer to detach itself from the ceramic body or the glass passivation layer.
In addition, a mechanical load is frequently applied to the contact area via the connecting wires. The mechanical forces acting on the contact area may have the effect that an already affected mechanical connection between the individual layers may perhaps be impaired still further, and this may lead to even stronger damage or, in the worst case, to destruction of the sensor component. The service life of the sensor component will, however, be markedly reduced in any case, and, if the sensor component is damaged, it may also happen that the detected measuring results are influenced or corrupted.
Jp 06-137959 A describes a platinum temperature sensor component in the case of which an extension conducting wire and its connection point to a main conducting wire are to be protected against breaking caused by bending in that the connection point is covered with an insulator having a certain strength, whereas the extension conducting wire is covered with a flexible coating.
Starting from this prior art, it is the object of the present invention to provide a sensor component with a more reliable and more resistant contact arrangement.
The object of the present invention is achieved by a sensor component according to claim 1 and by a method of producing a sensor component according to claim 8.
The sensor component of the present invention comprises a ceramic support, a metal film applied to the ceramic support, at least one connecting wire electrically connected to the metal film in a contact area, and a fixing glaze applied to the metal film and the at least one connecting wire in the contact area, the ceramic support of the sensor component having at least one recess in the area of the fixing glaze.
The present invention additionally provides a method of producing a sensor component comprising the following steps: applying a metal film to a ceramic support, providing at least one recess in the ceramic support, electrically connecting the metal film to at least one connecting wire in a contact area, applying a fixing glaze composition to the connecting wire, the metal film and the at least one recess in the contact area, and fusing the fixing glaze composition to the ceramic support.
The present invention is based on the finding that the contact quality between the sensor component and the lead-in wires can substantially be improved by providing additional mechanical interlocking between the fixing glaze and the ceramic support. This additional mechanical interlocking is achieved by providing recesses in the ceramic support during the production of the sensor component; also the metal film is removed at the locations of these recesses. These trenches are then filled with a suitable glass composition. When the connecting wires have been bonded to the contact surfaces provided, this contact area is encompassed by a fixing glaze composition and fused at a high temperature. In the course of this process, the fixing glaze composition will fuse not only with the platinum film but also with the glass composition arranged laterally to this platinum film in the recesses. The glass composition in the recesses can be formed by the fixing glaze composition itself or it can also be applied to the recesses separately prior to the fusion step, a uniform and permanent fixing of the connecting wires in the contact area of the sensor component being achieved by fusing the fixing glaze with the substrate support. The recesses in the ceramic material can, in addition, also be arranged on the front where the connecting wires leave the contact area.
One advantage of the present invention is to be seen in the fact that, due to the interlock between the fixing glaze composition and the ceramic support, a substantially improved mechanical stability of the contact between the connecting wires and the connection areas of the metal film is achieved in the contact area of the sensor component.
A further advantage of the present invention is to be seen in the fact that at the otherwise open lateral parting surface the metal film is completely and hermetically sealed against aggressive environmental influences, e.g. against an aggressive chemical atmosphere, by means of the sensor component arrangement according to the present invention, whereby the metal film will be prevented from detaching itself from the substrate support.
A further advantage of the present invention is to be seen in the fact that the adherence between the metal film and the ceramic support is prevented from loosening, whereby the contact quality between the metal film and the connecting wires will additionally be improved to a decisive extent. On the basis of these measures, a longer service life of the sensor component can be achieved even under extremely hard environmental conditions.
Preferred further developments of the present invention are defined in the subclaims.